This invention relates to an electrophotographic recording element comprising an electrically conducting support and a film of photoconductor material containing an organic electric charge generator compound derived from aniline sulphonephthalein. Recording elements for electrophotographic reproduction are known, in which a first layer, in contact with an electroconducting support, is formed from electric charge generator compounds based on pyrilium salts, and a second layer, superposed on the first, is formed from organic substances, the function of which is to transport the electric charges.
Such recording elements have certain drawbacks which limit their use, such as: very low sensitivity in the infrared radiation range; the need to use sophisticated and very costly spreading apparatus such as vacuum evaporators; poor mechanical strength of the films produced, with consequent surface deterioration during the development and transfer cycles; low photochemical stability to ozone and heat, with consequent reduction of the life of the photoconducting element with increase in the memory effect; and high toxicity of some of the compounds used. Sulphonephthalein derivatives are known as pH indicators and as single layer zinc oxide photoconductor sensitisers.
The sulphonephthalein derivatives used for sensitising zinc oxide are poorly soluble in the common solvents used in preparing electrophotographic zinc oxide paints, with the result that there is considerable difficulty in spreading a single photoconducting layer to perform both the functions of generating and transporting the electric charges.
Moreover, these photoconductors have very low sensitivity in the infrared radiation range.